Tumor vasculature is uniquely subject to the influence of products derived from the neoplastic cells. This may underlie the altered reactivity of vessels in certain tumors to catecholamines (1), tumor necrosis factor (TNF), flavone acetic acid (2), as well as other agents. To identify tumor-derived mediators which alter vascular function, the experiments described herein focussed on murine methylcholanthrene A (meth A)-induced fibrosarcomas. In vivo, this tumor is sensitive to TNF, and infusion of the cytokine at low concentrations results in vascular compromise localized to the neoplastic lesions with early thrombosis/hemorrhage in the vessels and increased vascular permeability, and later regression of the tumor (3-7). In contrast, cultured meth A tumor cells are relatively insensitive to TNF (3,8). This suggests that tumor-derived mediators, potentially acting at the level of the endothelium, a central regulator of vascular tone, permeability and thrombogenicity, could be important in host-tumor interactions.
These considerations have led to the study of supernatants of meth A fibrosarcoma cells in order to identify soluble factors which alter endothelial functions. Recently, the purification of an apparently unique polypeptide, M.sub.r .apprxeq.40,000, which alters endothelial and monocyte properties (Endothelial cell and Monocyte Activating Polypeptide, EMAP I) was reported (9-10). Reported here are the purification, N-terminal sequence, and characterization of another novel polypeptide from the same meth A fibrosarcoma supernatants, which alters endothelial and monocyte functions, induces the migration of monocytes and granulocytes, and induces an inflammatory response in the mouse footpad model. Because of these properties, this second polypeptide derived from meth A cells is termed endothelial-monocyte activating polypeptide II (EMAP II).
A prominent characteristic of immunogenic tumors is the presence of an inflammatory infiltrate surrounding the neoplastic lesion (103). One potentially important mechanism through which tumors modulate the host response is through the production of cytokines activating host effector cells, including mononuclear phagocytes (MPs), polymorphonuclear leukocytes (PMNs), and endothelial cells (ECs)(4-7). Using the murine methylcholanthrene A-induced fibrosarcomas (meth A) as a model system, three polypeptides with cytokine-like activities were identified (5-7). One of these is the murine homologue of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF)(6) which modulates properties of ECs, including growth and induction of the procoagulant cofactor tissue factor, and MPs, including cell migration and tissue factor expression (8-13). In addition, two distinct polypeptides from meth A-conditioned medium termed endothelial-monocyte activating polypeptides I and II were isolated (5,7). EMAP II, a novel .apprxeq.20 kDa polypeptide which has recently been cloned and is not a member of previously described cytokine/chemokine families, has multiple effects on ECs, MPs, and PMNs in vitro, and induces an acute inflammatory response upon subcutaneous injection into mice (7).
Protein sequence data from the N-terminal region of EMAP II (residues #10-20) indicated a close relationship to vonWillebrand factor antigen II (residues #480-490; 14-15), a molecule released by platelets and ECs along with vonWillebrand factor (16-17). Pilot studies with purified vonWillebrand antigen II showed that it had cytokine-like properties resembling EMAP II (18), leading to speculation that the region of strong sequence homology between the two molecules might mediate effects on target cells. Consistent with the possibility that the N-terminal position of EMAP II might be involved in its interaction with target cells is an homology to residues #31-37 of Interleukin (IL) 8, which includes the Glu-Leu-Arg motif associated with receptor binding and neutrophil activation by IL-8 (19-21). This study reports the synthesis of a series of peptides based on the N-terminal sequence of EMAP II (residues #6-20), and used these to perform experiments on cultured MPs and PMNs, and to inject into mouse footpads. The results support the hypothesis that this region of the molecule contributes to the functional activity of EMAP II. The N-terminal EMAP II-derived peptides interact with specific, potentially novel cellular binding sites, and may define a new ligand-receptor interaction important in tumor vasculature and inflammation.